Abstract: High-accuracy topographic data acquisition is the core task of the multibeam sounding system, and the quality factor (equivalent to the sounding accuracy) provided by the traditional method does not take into account the sounding quality assessment of the quadratic fitting phase detection. This paper first derives the condition of the phase difference in first and quadratic curve. From the perspective of statistics, the time-of-arrival estimated mean square error and the quality factor expressions for the quadratic fitting phase detection are then given, providing a reference for the parameter design of high-accuracy system. Simulation and sea-trial data processing results show that the quality factor can effectively evaluate the sounding results in real time, and the quantity of outliers can be reduced by 70% by eliminating them using the quality factor. In the application of complex seabed, combining amplitude and quadratic fitting phase detection with screening of the sounding results by quality factor produces results that are essentially consistent with those of the EM122 multibeam sounding system, and the sounding errors can be reduced by over 10% compared to combining amplitude and first fitting phase detection.